This invention relates generally to the manipulation of light carried by optical fibers. More particularly, the present invention relates to filtering light and propagating reflected light along optical paths of a planar lightguide circuit.
In recent years, the use of optical fibers has become increasingly widespread in a variety of applications. Optical fibers have been found to be especially useful for many industries such as telecommunications, computer-based communications, and other like applications.
To maximize efficiency of optical waveguides, multiple information channels can be multiplexed into a single optical beam. In other words, multiple channels of information can propagate along an optical waveguide as a single beam of light energy. In order to form the multiplexed optical signal or to demultiplex the optical signal, optical filters are typically employed to separate light energy of a first wavelength from light energy having different wavelengths. To maximize optical filter efficiency, light energy can be collimated such that rays of light forming an optical beam travel in a manner parallel with one another. Such a collimation of light energy enables individual rays to strike an optical filter at a desired angle. Without collimating light energy, individual rays of light could strike an optical filter at undesirable angles which reduces optical filter efficiency.
For example, in the conventional art as illustrated in FIG. 1, an expanded beam optics system 10 can be used to separate channels of information of a single optical beam 20 that propagates along an optical waveguide 15. Each channel of the single optical beam 20 can have a different wavelength. For example single beam 20 as illustrated in FIG. 1 can include separate information channels that are carried by a first optical beam having a wavelength of lambda sub one (xcex91) and a second optical beam having a wavelength of lambda sub two (xcex92).
The expanded beam optics system 10 can employ a lens 30 to collimate the beams of optical energy forming the single optical beam 20. The lens 30 is necessary hardware for the conventional system since whenever optical energy leaves one medium and enters into another medium the optical energy refracts or diverges because of the changes in the indices of refraction of the different materials. In addition to the lens 30, the expanded beam optics system 10 also uses free space 40 between an optical filter 50 and the lens 30. The free space 40 may be open space or it may include another medium such as a glass block (not shown).
In FIG. 1, a few of the optical beams 25 that form the single beam 20 are illustrated in order to demonstrate that the individual optical beams 25 are substantially parallel with one another when exiting the lens 30. When the individual optical beams 25 strike the optical filter 50, only optical beams of a predetermined wavelength are permitted to pass through the optical filter 50. In the example illustrated in FIG. 1, the optical filter is designed to pass only optical beams having a wavelength of lambda one (xcex91). The individual optical beams 25 having a wavelength of lambda one (xcex91) pass through the optical filter 50 and through a glass plate 60 that supports the optical filter 50. The filtered optical beam 70 exits the glass plate 60. The light reflected off of optical filter 50 has optical beams that have wavelengths other than lambda one (xcex91), such as lambda two (xcex92).
One of the drawbacks of the conventional art is that with such a traditional optics systems 10 larger mechanical configurations are required. In other words, the lens 30 is typically large and bulky relative to the size of the optical waveguide 15. Furthermore, the amount of collimation for light energy with a lens 30 can be directly related to the cross sectional area of the optical beam. Expanded beam optics systems 10 require precision alignment and mounting of the optical devices relative to each other. In other words, the optical waveguide 15 must be in precise alignment with the lens 30 to promote optical efficiency. Similarly, the lens 30 must be in precise optical alignment with the optical filter 50 in order to also promote optical efficiency. Such configurations are not cost efficient for mass production. Additionally, much optical signal loss can occur between the waveguide-lens interface an the lens-free space interface.
Accordingly, a need in the art exists for separating optical energy into separate optical beams of different wavelengths with a higher efficiency. There is a further need in the art for a system for separating optical energy that can optimize the transfer of single mode optical energy propagation between an optical waveguide and a filtering device. An additional need in the art exists for a system that can tolerate a certain amount of misalignment between optical hardware without introducing substantial optical losses. Another need exists in the art for a system separating optical energy that can be easily manufactured and scaleable smaller sizes compared to traditional expanded beam optics that require a substantial amount of hardware. Another need exists in the art for a system for separating optical energy without the use of lenses.
The present invention solves the problems of expanded beam optics systems by providing an optical network assembly that includes a planar lightguide circuit (PLC) and a filtering device. A PLC can have at least two optical paths for propagating optical energy. The PLC can be designed to channel optical energy to the filtering device in order to separate the optical energy into at least two beams, where a first beam can contain a first information channel and a second beam can contain a second information channel. The filtering device can be attached directly to the PLC or it can be attached directly to an optical waveguide that is also connected to the PLC. This direct attachment can be accomplished by building up the filtering device on the PLC or on the optical waveguide with a thin film deposition process. The optical waveguide can be a flexible optical fiber that is part of a communications network. The optical waveguide can either feed optical energy to or propagate optical energy away from the PLC. Multiple optical waveguides can be attached to a PLC to feed optical energy into and away from the PLC.
Each optical path of a PLC can be made of a transparent core of relatively high refractive index, light-conducting material while the planar material surrounding an optical path can be made of a medium having a lower refractive index. The optical paths can be made of silica, plastic, glass, or low-to-no expansion optical material such as ZERODUR glass. Each of the optical waveguides can be made of materials similar to a PLC. Both the optical waveguides and PLCs can be designed to propagate single modes of optical energy such that the optical energy travels as a single wavefront in order to reduce attenuation and other undesirable effects while increasing bandwidth and transmission properties such as increases in traveled distances.
A PLC or a filtering device (or both) can optimize transfer of single mode optical energy propagation (referred to as modal transfer) between an optical waveguide and the PLC. The PLC and filtering device can be designed to minimize modal disruption (such as changes in E-Field geometry) of optical energy that can occur during the modal transfer of the optical energy between an optical waveguide and the PLC. A PLC can minimize modal disruption that occurs within an interface or junction between the PLC and another light carrying device by facilitating efficient alignment between the PLC and the other light carrying device.
In other words, a PLC""s geometry permits rapid and efficient allignment between a PLC and another light carrying device such as an optical waveguide. A PLC in combination with another light carrying device can tolerate a certain amount of misalignment relative to each other without introducing substantial optical losses. This tolerance of misalignment can also increase manufacturability of an optical system that includes a PLC since dimensioning of both a PLC and other light carrying device can be relaxed.
Furthermore, a PLC can permit the use of passive alignment techniques that can reduce time as well as expense compared to conventional active alignment techniques that require signal propagation measurements. That is, with passive alignment, signal propagation testing can be substantially eliminated. Additionally, PLCs can be scaled to smaller sizes compared to traditional expanded beam optics that require additional hardware such as lenses. PLCs can interact with filtering devices without the use of lenses that are typically required in traditional optics to collimate optical energy.
Similar to a PLC, a filtering device in combination with a PLC can optimize the modal transfer between a PLC and another light carrying device. One way to optimize modal transfer between a light carrying device and a PLC is to deposit the filtering device directly on the PLC itself or the light carrying device that can be connected to the PLC. Another way to optimize modal transfer between a light carrying device and a PLC is to reduce a thickness of the filtering device such that optical energy can be transferred to or away from a PLC in the near field. In other words, by reducing the thickness of a filtering device, divergence of optical energy propagating through the filtering device can be reduced or become negligible because the interface between the PLC and light carrying device is substantially small such that optical energy is essentially channeled in a waveguide between the light carrying device and PLC.
Another way to optimize the modal transfer of optical energy between a light carrying device and a PLC is to provide modal adaptations such as changes in geometry in the vicinity of the PLC-light carrying device junction in order to shape the actual mode fields of optical energy. For example, the cross sectional geometry of the either the PLC or light carrying device or both can be adjusted to match each other such that the mode field propagated by the PLC matches the mode field propagated by the light carrying device.
A filtering device can optimize modal transfer between a light carrying device and a PLC by increasing the packing density of the filtering device such that the filtering device approaches a bulk density. In other words, an increased packing density of a filtering device can substantially reduce or eliminate voids within the filtering device that interfere with the propagation of optical energy. Such voids can trap light reflecting or light disturbing materials such as water vapor.
The PLC and filtering device can form building blocks for more complex optical networks or network architectures. In one aspect of the present invention, a PLC and filtering device combination can form a drop or add configuration where one channel of information propagating within a multichannel or multiplexed optical beam can be either dropped from or added to the multichannel or multiplexed beam. In another aspect, the PLC and filtering device combination can form a single channel drop-add configuration where one channel can be dropped from a first multichannel optical beam and then added to a second multichannel optical beam.
In yet another aspect, optical paths within a PLC can be non-linear or curved in order to provide control over an angle of incidence of an optical beam striking the filtering device to minimize obliqueness. The PLC and filtering device combination can form a waveguide-constrained cascade where the PLC can include multiple optical paths that lead to a plurality of filtering devices. Such waveguide-constrained cascades can either multiplex or demultiplex optical energy that propagates through light carrying devices. The PLC and filtering device combination can multiplex separate optical beams having individual channels into a single optical beam or demultiplex a single optical beam into separate optical beams with distinct or different channels.
In another aspect, the PLC and filtering device combination can include multiple mirrors coupled to the PLC that re-direct optical energy onto a plurality of filtering devices. This can refocus optical energy in order to re any optical beam divergence as the optical energy reflects off of a filtering device. Alternatively, the PLC and filtering device combination can form a daisy-chained path waveguide that can optimize positioning or allignment of the optical paths of a PLC with a plurality of filtering devices.
In a further aspect, the PLC and filtering device combination can form a remotely configurable drop-add plus optical cross connect network. The PLC and filtering device combination can further include an activating or diverting element such as a moving mirror that diverts a channel signal out of an optical circuit while introducing a new signal content along the same channel into the optical circuit. This embodiment can function as an optical switch.
For an additional aspect the PLC and filtering device combination form a part of an amplification or gain flattening architecture. Gain flattening elements can be inserted into light paths outside of the PLC and filtering device combination to discretely attenuate channels which in turn flattens the gain of an optical signal over an extended spectral range.
Similar to how the PLC and filtering device combination can form building blocks for optical network architectures, the multiplex, demultiplex, and the optical drop-add inventive concepts can form building blocks for even larger network architectures. These larger network architectures can include a multiplex-demultiplex configuration and an optical drop-add configuration. In a multiplex-demultiplex configuration, multiple beams that each carry a unique information channel can be combined or multiplexed into a single optical beam. This single optical beam can then be propagated along a light carrying device to another PLC and filtering device combination that can then demultiplex the single optical beam into multiple optical beams. In the optical drop-add configuration, multiple channels can be multiplexed into a single optical beam and a few channels can be dropped or added or both at a point between two PLC-filtering device combinations that multiplex and demultiplex the single optical beam.
The PLC and filtering device combination, in addition to the multiplex-demultiplex configuration and optical drop-add configuration, can form an optical cross-connect configuration that permits the sharing of optical channels between at least two separate optical networks. The PLC can be formed with a single segment of optical material suitable for an optical waveguide. A sharp bend of an appropriate angle can be introduced into the single segment of optical material that the PLC and the optical waveguide form an integral unit.
A PLC can be integrated into a bulk matrix. This structure can be formed by utilizing polymer molding techniques such as insert injection molding or by planar waveguide fabrication.
The PLC and filtering device combination can further optimize modal transfer of optical energy by manipulating the shape of the optical paths disposed within a PLC. In other words, an optical path of a PLC can be shaped in such a way as to minimize the divergence of optical energy as the optical energy passes through the filtering device. An optical path within a PLC can be tapered so that optical energy is projected optimally through the filtering device and into a fiber core of an optical waveguide. The shaping of optical paths within a PLC can reduce losses that can occur when optical energy propagates through the filtering device.
The PLC and filtering device combination can be part of mounting structures that facilitate the precise alignment of light carrying devices such as optical waveguides with each PLC and filtering device. These mounting structures can include blocks comprising cavities having a shape similar to a respective PLC. Other mounting structures can include V-groove based assemblies that are designed to align optical waveguides by supporting the outer cladding of optical waveguides with a respective V-groove. The V-grooves can be made at appropriate angles relative to one another as dictated by the number of optical wage guides to be coupled and the type of PLC and filtering device being employed.
That the present invention improves over the drawbacks of the conventional art and accomplishes the objects of the invention will become apparent from the detailed description of the illustrative embodiments to follow.